Circuits and methods for controlling a tracking actuator of an optical disk player

ABSTRACT

A digital servo circuit for an optical disk player having a tracking actuator utilizes a digital filter for alternately extracting from a tracking error signal a frequency component within a specified band and a high-frequency component. In response to the high-frequency component, a braking force is applied to the tracking actuator when a brake ON command is issued. Coefficient values in the digital filter are set up depending on whether the brake ON command is issued.

This is a divisional of application Ser. No. 08/257,473, filed Jun. 9,1994, now U.S. Pat. No. 5,623,465, which is a continuation of U.S.patent application Ser. No. 07/971/897 filed Nov. 4, 1992, nowabandoned.

FIELD OF THE INVENTION

The present invention relates to an optical disk player using a digitalservo-control circuit and, more particularly, to a digital servo circuithaving servo control functions for tracking servo, focus servo, andthread servo. It further relates, with respect to a tracking servocircuit, to an optical disk player using a digital servo circuit havingan anti-shock function.

DESCRIPTION OF THE RELATED ART

When a defect is present in the signal surface of a disk in a trackingor focus servo circuit of an optical disk player such as a CD player,there is a possibility that a normal error signal becomes unobtainableand an out-of-servo state is brought about. Therefore, when a defect isdetected, it is practiced to use a pseudo error signal instead of eacherror signal to stabilize the servo. As the pseudo error signal, a lowfrequency component of each error signal obtained immediately before thedetection of the defect is used. Therefore, each servo circuit isprovided with an LPF (low-pass filter) for extracting the low-frequencycomponent from each error signal.

The optical pickup for reading information from the signal surface of adisk is controlled for its position in the radial direction of the diskby a thread servo circuit. In the thread servo circuit, a low-frequencycomponent of the tracking error signal is used for the driving signal ofa thread motor as the driving unit of the optical pickup. Accordingly,an LPF is required also in the thread servo circuit for extracting alow-frequency component from the tracking error signal.

When it is considered to construct a digital arrangement of the servocircuits having such various filters, there arises a problem, if thefilters should be provided independently of one another, that the stepsof DSPs (digital signal processors) increase and the scale of thecircuit expands.

As a tracking servo circuit, that arranged as shown in FIG. 1 ishitherto known. Referring to FIG. 1, recorded information on a disk 1 isread by an optical pickup 2 and the read RF signal is supplied to thedemodulation system through an RF amplifier 3 and supplied also to atrack-crossover detector 5 after being digitized in an A/D converter 4.A tracking error (TE) signal generator 6 generates a tracking errorsignal having the so-called S-curve characteristic through such ageneration method as the well-known three-beam method according to theoutput of the optical pickup 2. The tracking error signal is passedthrough the A/D converter 4 and supplied to a servo filter 7, ananti-shock BPF (bandpass filter) 8, and an HPTZC (High Pass TrackingZero Cross) HPF (high-pass filter) a. The tracking error signal passedthrough the servo filter 7 is supplied to a PWM generator 10.

The PWM generator 10, as shown in FIG. 2, is adapted to select eitherthe tracking error value passed through a servo register 21 in a servoON state or a jump value from a jump value register 22 by means of aselector switch 23 in response to a track-jump command issued at thetime when a track-jump operation is to be made and supply the selectedvalue to a PWM pulse generator 25 through an AND gate 24. In the servoON state, the tracking error signal is turned into a pulse correspondingto its signal level, and the pulse is supplied, through an actuatordriver 11, to a tracking actuator in the optical pickup 2 as a drivingsignal. Thereby, the position of the information reading optical spot inthe radial direction of the disk with respect to the track (pit string),from which information is being read, of the disk 1 is controlled.

When a track-jump command is issued from a μCPU (microcomputer) 12, thePWM generator 10 generates a jump pulse with a pulse width correspondingto the number of tracks which the information reading light spot has tocross over according to a jump value output from the jump value register22 and supplies the pulse to the tracking actuator through the actuatordriver 11. During the jump operation, the servo is in an OFF state.

In the anti-shock BPF 8, only a frequency component of a specifiedfrequency band is extracted from the tracking error signal. Theextracted frequency component of the specified frequency band issupplied to a comparator 13 to be compared with a predeterminedreference level. The comparison output is supplied to the servo filter 7as a gain changeover signal. Then, if there is present an amplitude at ahigher level than the reference level in the specified frequency band ofthe tracking error signal, it is determined that a vibration hasoccurred and control is exercised so that the gain of the servo filter 7is raised. More specifically, when a vibration occurred in a CD player,especially in a portable type CD player, the vibration is detected andthe gain of the servo filter 7 is raised, whereby it is made so that anout-of-servo state is hardly brought about. This is the so-calledanti-shock function. Whether or not execution of the anti-shock functionis selected is determined depending on whether or not an anti-shock ONsignal for activating the anti-shock BPF 8 is output from the μCPU 12.

The phase of the tracking error signal is advanced by being passedthrough the HPTZC HPF 9 and turned into an HP (High-pass) TZC (TrackingZero Cross) signal by being sliced in a slicer 14 taking the zero levelas the slice level. The HPTZC signal is supplied to an edge detector 15and its edge is detected therein. The HPTZC edge signal is supplied to asampling circuit 17 for sampling a mirror signal at a high leveloriginated from the mirror surface between tracks on the disk 1 andgenerated by a mirror signal generator 16. The sampling signal issupplied to the PWM generator 10 as a tracking cancel signal.

Referring to FIG. 2 again, the inverted signal of the track jump signalinverted by an inverter 26, a brake ON signal issued from the μCPU 12,and the tracking cancel signal output from the sampling circuit 17constitute three inputs of an AND gate 27. The output of the AND gate 27is supplied to the AND gate 24 as a mask signal and serves as a gatecontrol signal of the AND gate 24. More specifically, the trackingcancel signal is rendered effective and serves as the mask signal whenthe brake ON command is issued while there is no issuance of thetrack-jump signal.

Thus, as shown in FIG. 3, the tracking cancel signal is renderedeffective immediately after a track jump has been performed, and themask signal following it masks only the tracking drive signal waveformof the polarity corresponding to the track jump. As a result, a force inthe opposite direction to that of the track jump, i.e., a braking force,is applied to the tracking actuator immediately after the jump has beenperformed.

During the truck jump operation, it is detected by the track-crossoverdetector 5 that the information reading light spot has crossed over atrack according to the RF signal and the tracking error signal and, upondetection of it, a count out signal Gout is issued. Then, the μCPU 12detects the track at the destination of the jumping by counting thecount out signal Gout.

In the digital tracking servo circuit as described above, when theanti-shock BPF 8 is independently constructed using its own individualDSP (Digital Signal Processor) step, the DSP step becomes insufficientif the existing sampling rate (for example 88.2 KHz) is used. Hence, thesampling rate is decreased to save the DSP steps. However, decrease inthe sampling rate invites complexity of the circuit configuration and,further tends, when the circuit is arranged in an IC, to deteriorate theperformance of the IC as a whole.

SUMMARY OF THE INVENTION

A digital servo circuit according to the present invention comprises adefect detector for detecting a defect in the signal surface of anoptical disk according to a read signal from the signal surface, adigital filter for sequentially extracting a first low-frequencycomponent and a second low-frequency component from a tracking errorsignal and a low-frequency component from a focus error signal on atime-sharing basis according to coefficient-values set up therein,coefficient setting means for sequentially setting up predeterminedcoefficient values in the digital filter in synchronism with itstime-sharing operation, a thread servo circuit for controlling anoptical pickup for its position in the radial direction of the diskaccording to the first low-frequency component of the tracking errorsignal, a hold register for tracking for holding the secondlow-frequency component of the tracking error signal, a hold registerfor focusing for holding the low-frequency component of the focus errorsignal, a tracking servo circuit for controlling an information readinglight spot for its position in the radial direction of the disk withrespect to the track of the optical disk, along which the information isbeing read, responding to the tracking error signal and, when a defecthas been detected by the defect detector, responding to the output heldin the hold register for tracking instead of responding to the trackingerror signal, and a focus servo circuit for controlling an objectivelens incorporated in the optical pickup responding to the focus errorsignal so that the distance of the objective lens from the signalsurface of the optical disk remains constant and, when a defect has beendetected by the defect detector, responding to the output held in thehold register for focusing instead of responding to the focus errorsignal.

in the digital servo circuit, which requires a filter for thread servoand filters for defect holding for tracking and for focusing, arrangedas described above, since the frequency band of these filters is low andit is possible to decrease the sampling rate of them, it is realized toprovide a single digital filter in terms of hardware with functions of aplurality of filters by allowing each of these filters to operate forexample once for each 256 DSP periods and sequentially changing thecoefficient values of multiplying coefficients of a digital filter and,thereby, utilizing the digital filter on a time-sharing basis.

The present invention, directed to the provision of a tracking servocircuit for an optical disk player capable of reducing the circuit scaleby saving the DSP steps and achieving a high sampling rate, comprises adigital filter for leading out a frequency component front a specifiedband and a high-frequency component of the tracking error signal in analternative way according to coefficient values set up therein, gaincontrol means for executing control, when the signal level of thefrequency component of the specified band is higher than a specifiedreference level, to raise the servo gain, actuator control meansapplying a braking force to the tracking actuator using thehigh-frequency component when a brake ON command is issued, andcoefficient setting means for setting up predetermined coefficientvalues in the digital filter depending on whether or not the brake ONcommand is issued. Thus, by changing the setting of coefficient valuesin the digital filter depending on whether or not the brake ON commandis issued, a single digital filter can be provided with both thefunctions of a High Pass Tracking Zero Cross HPF and an anti-shock BPFand both the filters can be formed on the same DSP step. As a result, itbecomes possible to save the DSP steps and reduce the circuit scale and,further, to achieve a high sampling rate.

BRIEF DESCRIPTION OF TEE DRAWINGS

FIG. 1 is a block diagram showing a structure of a conventional exampleof a tracking servo circuit;

FIG. 2 is a block diagram showing a structure of a conventional PWMgenerator;

FIG. 3 is a waveform chart showing relationships between a trackingdrive waveform and various commands in a conventional example;

FIG. 4 is a block diagram showing an embodiment of a digital servocircuit according to the present invention;

FIG. 5 is a structural diagram showing a digital filter according to thepresent invention;

FIG. 6 is a block diagram showing a structure of the main part of atracking servo circuit as a second embodiment of the present invention;

FIG. 7 is a structural diagram of a digital filter as an anti-shock BPF;and

FIG. 8 is a structural diagram showing a digital filter as a High PassTracking Zero Cross HPF.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

An embodiment of the present invention will be described below in detailwith reference to the accompanying drawings.

FIG. 4 is a block diagram showing an embodiment of a digital servocircuit according to the present invention. Referring to FIG. 4,recorded information on a disk 1 is read by an optical pickup 2. Theoptical pickup 2 is operatively arranged for movement in the radialdirection of the disk 1 with a thread motor 43 used as the driving unit.An RF signal read by the optical pickup 2 is passed through an RF signalgenerator 44 and supplied to the demodulation system and also digitizedin an A/D converter 45 and becomes the detection input of a defectdetector 46. The defect detector 46 is for detecting a defect such as asmear on or absence of pits in the signal surface of the disk 1.

A focus error (FE) signal generator 47 generates a focus error signal bysuch a generation method as the well-known astigmatic method, while atracking error (TE) signal generator 48 generates a tracking errorsignal by such a generation method as the well-known three-beam method.The focus error signal and the tracking error signal are selectivelysupplied to a focus servo filter 51 and a tracking servo filter 52through changeover switches 49 and 50, respectively.

The focus error signal and the tracking error signal passed through theservo filters 51 and 52 are supplied to PWM generators 53 and 54,respectively. The PWM generator 53 for focusing, in a servo ON state,turns the focus error signal into a pulse corresponding to the signallevel of the focus error-signal and supplies the pulse to a focusactuator in the pickup 2 as the drive signal through an actuator driver55. Thereby, the position of an objective lens incorporated in theoptical pickup 2 in the direction perpendicular to the signal surface(in the direction of the optical axis) is controlled such that theinformation reading optical spot is brought into a just-focused statewith respect to the signal surface of the disk 1.

The PWM generator 54 for tracking, in the servo ON state, turns thetracking error signal into a pulse corresponding to the signal level ofthe tracking error signal and supplies the pulse to a tracking actuatorin the pickup 2 as the drive signal through an actuator driver 56.Thereby, the position of the information reading light spot in theradial direction of the disk with respect to the track (pit string) ofthe track 1, along which information is being read, is controlled.

The tracking error signal is further passed through an analog LPF 57 foreliminating the folding noise in A/D conversion and digitized in an A/Dconverter 58 and becomes two inputs of a multiplexer (MPX) 59 with threeinputs and a single output. To the remaining input of the multiplexer 59is supplied a low-frequency component of the focus error signal led outfrom the intermediate stage of the focus servo filter 51. The output ofthe MPX 59 is supplied to a digital filter 60.

The digital filter 60, as shown in FIG. 5, is arranged such that thecoefficients K1 to K3 of its multiplying coefficients can be arbitrarilyset up according to coefficient data output from a coefficient RAM 61.The coefficient RAM 61 reads the coefficient data stored at addressesspecified by address signals output from an address generator 62 andoutputs the coefficient data to the digital filter 60. The addressgenerator 62 sequentially outputs predetermined address signals to thecoefficient RAM 61 when count values for example of an 8-bit counter 63,which counts up by one for example each period of 88.2 KHz, are FF, 00,01 (Hex), for example.

Thereby, three sequences of coefficient data are supplied from thecoefficient RAM 61 to the digital filter 60 successively and cyclicallyat predetermined intervals. That is, the digital filter 60 functions asthree systems of LPF on a time,sharing basis. The LPF of the firstsystem is the filter for thread servo, which extracts a low-frequencycomponent of the tracking error signal with the filter characteristicbased upon the coefficient values set up therein and supplies thelow-frequency component to a PWM generator 64 so as to be turned thereininto a pulse corresponding to its signal level and, then, passed througha thread driver 65 to become the drive signal for a thread motor 43.

The LPFs of the second and third systems are the filters for defectholding which extract low-frequency components of the tracking errorsignal and the focus error signal and store the low-frequency componentsof the error signals into hold registers 66 and 67, respectively. When adefect of the disk 1 is detected by the defect detector 46, thechangeover switch 49 is switched by the detection output and the heldoutput by the hold register 67 is supplied as a pseudo error signal tothe servo filter 51 instead of the focus error signal and, thereby, theplayer is prevented from going into an out-of-servo state due to adefect in the signal surface of the disk 1. The same is true with thetracking servo.

When the three systems of filters, i.e., the filter for thread servo,and the defect holding filters for focusing and tracking, are supposedto be independent units of one another when, for example, DSPs arearranged in 64 steps with respect to the master clock at 5.6448 MHz,each filter operates having 88.2 KHz taken as one cycle. However, thefrequency band required of each filter is quite lower than 88.2 KHz. Ifsampling is performed at 88.2 KHz, the bits of coefficients andmultipliers greatly increase in number.

Hence, in the present invention, the operations of the thread servofilter and the focus and tracking defect holding filters are decimated,i.e., they are arranged to operate once every 256 periods. Thereby,these filters are arranged to perform their sampling at 345 Hz insubstance and the bits of the coefficients and multipliers can beprevented from increasing in number. Conversely, each filter operatesonly once for 256 periods. Hence, by utilizing the digital filter 60 ona time-sharing basis, it becomes possible to incorporate a plurality offilters into the filter, which is a single filter in terms of hardware.Thus, the number of steps of the DSP can be saved and accordingly thecircuit scale can be reduced.

A second embodiment of the present invention will be described in detailwith reference to the drawings.

FIG. 6 is a block diagram showing the second embodiment of the presentinvention, in which the structure of only the main portion of a trackingservo circuit according to the present invention is shown. In FIG. 6,there is provided a single digital filter 31, which accepts the trackingerror signal, corresponding to the anti-shock BPF 8 and the High PassTracking Zero Cross HPF 9 shown in FIG. 1. The digital filter 31 isarranged such that the coefficient value of each multiplying coefficientcan be arbitrarily set up therein according to coefficient data outputfrom a coefficient RAM 32.

The coefficient RAM 32 reads coefficient data stored at addressesspecified by address signals generated by an address generator 33 andsupplies them to the digital filter 31. The address generator 33supplies the coefficient RAM 32 with two sequences of address signalscorresponding to the anti-shock BPF and the High Pass Tracking ZeroCross HPF in response to an address changeover signal.

Meanwhile, 4-bit (D1 to D4) commands for controlling the tracking servoare issued from the μCPU 12 and the commands are stored into a commandregister 34. Of the commands D1 to D4, D4 is a control command for theanti-shock function, D3 is that for providing brake, and D2 and D1 arethose for tracking gain UP. More specifically, anti-shock ON control iseffected when the commands (D4 to D1) are (10**), anti-shock OFF controlis effected when they are (0***), brake ON control is effected when theyare (*1***), brake OFF control is effected when they are (*0**),tracking gain Normal control is effected when they are (**00), andtracking gain UP control is effected when they are (**01), (**10), and(**11).

Hence, the output of an AND gate 36 having the command signal D4 and thecommand signal D3 inverted by an inverter 35 as its two inputs becomesan anti-shock ON signal to be supplied to the address generator 33 asthe address switchover signal, the command signal D3 as it is becomesthe brake ON signal, and the command signals D2 and D1 are passedthrough an OR gate 37 and the output becomes the tracking gain UPsignal.

When the anti-shock ON command (10**) is issued, the anti-shock ONsignal is output and, at the same time, the address signal correspondingto the anti-shock BPF is output from the address generator 33.Thereupon, the coefficient data corresponding to the address signal isoutput from the coefficient RAM 32 to the digital filter 31. As aresult, the digital filter 31 comes to constitute an anti-shock BPF by acombination of an HPF in the front stage and an LPF in the rear stage asshown in FIG. 7 and extracts a frequency component of a specified bandfrom the tracking error signal.

When, on the hand, the brake ON command (*1**) is issued, the brake ONsignal is output and, at the same time, the anti-shock ON signaldisappears. Hence, an address signal corresponding to the High PassTracking Zero Cross HPF is generated by the address generator 33 and thecoefficient RAM 32 outputs the coefficient data specified by the addresssignal to the digital filter 31. As a result, the digital filter 31comes to constitute a High Pass Tracking Zero Cross HPF, of which onlythe HPF in the front stage is rendered effective as shown in FIG. 8, andextract a high-frequency component from the tracking error signal.

As described above, the digital filter 31 has both functions of theanti-shock BPF and the High Pass Tracking Zero Cross HPF and is arrangedsuch that both the filters are provided on the same DSP step. Itfunctions as the anti-shock BPF in the anti-shock ON state and as theHigh Pass Tracking Zero Cross HPF in the brake ON state. Referring toFIG. 7 and FIG. 8, the multiplying coefficients K1 to K10 of themultipliers are predetermined coefficient values to be set up accordingto coefficient data output from the coefficient RAM 32.

Now, the anti-shock function is for bringing the servo filter 7 to again UP state, which means that the anti-shock function is not necessarywhen the servo filter 7 is already in the gain UP state. Further, sincethe servo filter 7 must be in the gain UP state when brake ON iseffected immediately after a track jump, it is a general practice thatthe command for tracking gain UP is issued simultaneously with the brakeON command from the μCPU 12.

More specifically, since the servo filter 7 has already been in the gainUP state when the brake ON command is issued, the anti-shock BPF is notnecessary during this time. In other words, the function of the HighPass Tracking Zero Cross HPF needed in the brake ON state and thefunction of the anti-shock BPF needed in the tracking gain Normal stateare not performed simultaneously.

The above fact was taken into consideration in making this invention andit is adapted therein such that, while the digital filter 31 is allowedto function as an anti-shock BPF in the state of anti-shock ON, thedigital filter 31 is not allowed to function as the anti-shock BPF whenthe brake ON command (*1**) is rendered active even if the anti-shock ONcommand (10**) is active, but allowed to function as a High PassTracking Zero Cross BPF.

By arranging such that the digital filter 31 is used either as the HighPass Tracking Zero Cross HPF or as the anti-shock BPF depending onpresence or absence of the brake ON command, in spite of the anti-shockcommand being active, as described above, it has been made possible toprovide both the filters in the same DSP step. Thereby, the DSP stepscan be greatly saved, namely, by using only 64 steps of the DSP steps,64 steps of servo functions for each of focusing, threading, and otherscan be realized and, hence, the circuit scale can be reduced. Besides,the sampling rate can be kept high (for example, at 88.2 KHz).

What is claimed is:
 1. A tracking servo circuit of an optical diskplayer having a tracking actuator for displacing an information readingoptical spot in the radial direction of an optical disk with respect toa track of the optical disk along which the information is read, thetracking servo circuit operative to execute drive control of saidtracking actuator according to a tracking error signal, comprising:adigital filter for alternately extracting from said tracking errorsignal a frequency component within a specified band and ahigh-frequency component according to coefficient values set up withinsaid digital filter; actuator control means for applying a braking forceto said tracking actuator in response to said high-frequency componentwhen a brake ON command is issued; and coefficient setting means forsetting up the coefficient values in said digital filter depending onwhether said brake ON command is issued; and an AND gate having anoutput coupled to the coefficient setting means, a first input coupledto an anti-shock control command and a second input coupled to aninverted brake control command.
 2. The tracking servo circuit of claim1, wherein said coefficient setting means comprises:an addressgenerator; and a coefficient memory.
 3. The tracking servo circuit ofclaim 1, wherein said coefficient values set up by said coefficientsetting means are predetermined.
 4. The tracking servo circuit of claim1, further comprising:an inverter having its output coupled to thesecond input of the AND gate; a register operative to receive and storean anti-shock control command, a brake control command and at least onetracking gain control command, the register having a first outputcoupled to provide the anti-shock control command to the first input ofthe AND gate and a second output coupled to provide the brake controlcommand to an input of the inverter.
 5. The tracking servo circuit ofclaim 4, wherein two tracking gain control commands are received andstored by the register, further comprising:an OR gate having a firstinput coupled to a third output of the register and a second inputcoupled to a fourth output of the register.
 6. The tracking servocircuit of claim 5, wherein said coefficient setting means comprises:anaddress generator; and a coefficient memory.
 7. A tracking servo circuitof an optical disk player having a tracking actuator for displacing aninformation reading optical spot in the radial direction of an opticaldisk with respect to a track of the optical disk along which theinformation is read, the tracking servo circuit operative to executedrive control of said tracking actuator according to a tracking errorsignal, comprising:a digital filter for alternately extracting from saidtracking error signal a frequency component within a specified band anda high-frequency component according to coefficient values set up withinsaid digital filter; actuator control means for applying a braking forceto said tracking actuator in response to said high-frequency componentwhen a brake ON command is issued; an address generator coupled to acoefficient memory operative to set up the coefficient values in saiddigital filter depending on whether said brake ON command is issued; anAND gate having an output coupled to an input of the address generator;an inverter having its output coupled to a first input of the AND gate;a register operative to receive and store an anti-shock control command,a brake control command and at least two tracking gain control commands,the register having an anti-shock control command output coupled to asecond input of the AND gate and a brake control command signal outputcoupled to an input of the inverter; and an OR gate having a first inputcoupled to a first tracking gain command output of the register and asecond input coupled to a second tracking gain command output of theregister.
 8. A method of controlling a tracking actuator of an opticaldisk player in accordance with a tracking error signal, the trackingactuator operative to displace an information reading optical spot inthe radial direction of an optical disk with respect to a track of theoptical disk along which the information is read, the method comprisingthe steps of:alternately extracting from said tracking error signal afrequency component within a specified band and a high-frequencycomponent according to coefficient values set up within a digitalfilter; applying a braking force to said tracking actuator in responseto said high-frequency component when a brake ON command is issued;setting up the coefficient values in said digital filter depending onwhether brake ON command is issued, wherein the step of setting up thecoefficient values in said digital filter comprises the steps ofgenerating addresses, reading coefficient data specified by saidaddresses, and supplying said coefficient data to said digital filter;and generating an address changeover signal in response to the existenceof both an anti-shock command and the non-existence of a brake ONcommand.
 9. The method of claim 8, further comprising the stepof:predetermining coefficient values to be set up.
 10. The method ofclaim 8, further comprising the steps of:storing a brake controlcommand; and inverting the brake control command.
 11. The method ofclaim 10, further comprising the steps of:storing a first tracking gaincommand; storing a second tracking gain command; and generating atracking gain up control signal when either of the stored first andsecond tracking gain control commands is in an UP state.
 12. A method ofcontrolling a tracking actuator of an optical disk player in accordancewith a tracking error signal, the tracking actuator operative todisplace an information reading optical spot in the radial direction ofan optical disk with respect to a track of the optical disk along whichthe information is read, the method comprising the steps of:alternatelyextracting from said tracking error signal a frequency component withina specified band and a high-frequency component according to coefficientvalues set up within a digital filter; applying a braking force to saidtracking actuator in response to said high-frequency component when abrake ON command is issued; generating addresses; reading predeterminedcoefficient data specified by said addresses; supplying said coefficientdata to said digital filter; storing a brake control command; invertingthe stored brake control command; generating an address changeoversignal in response to the existence of both an anti-shock command andthe non-existence of a brake ON command; storing a first tracking gaincommand; storing a second tracking gain command; and generating atracking gain up control signal when either of the stored first andsecond tracking gain commands is in an UP state.
 13. A tracking servocircuit of an optical disk player having a tracking actuator fordisplacing an information reading optical spot in the radial directionof an optical disk with respect to a track of the optical disk alongwhich the information is read, the tracking servo circuit operative toexecute drive control of said tracking actuator according to a trackingerror signal, comprising:a digital filter for alternately extractingfrom said tracking error signal a frequency component within a specifiedband and a high-frequency component according to coefficient values setup within said digital filter; actuator control means for applying abraking force to said tracking actuator in response to saidhigh-frequency component when a brake ON command is issued; andcoefficient setting means for setting up the coefficient values in saiddigital filter depending on whether said brake ON command is issued; anda gate having an output coupled to the coefficient setting means, afirst input coupled to an anti-shock control command and a second inputcoupled to an inverted brake control command.
 14. The tracking servocircuit of claim 13, wherein said coefficient setting means comprises:anaddress generator; and a coefficient memory.
 15. The tracking servocircuit of claim 13, wherein said coefficient values set up by saidcoefficient setting means are predetermined.
 16. The tracking servocircuit of claim 13, further comprising:an inverter having its outputcoupled to the second input of the gate; a register operative to receiveand store an anti-shock control command, a brake control command and atleast one tracking gain control command, the register having a firstoutput coupled to provide the anti-shock control command to the firstinput of the gate and a second output coupled to provide the brakecontrol command to an input of the inverter.
 17. The tracking servocircuit of claim 16, wherein two tracking gain control commands arereceived and stored by the register, and wherein the gate is a firstgate, further comprising:a second gate having a first input coupled to athird output of the register and a second input coupled to a fourthoutput of the register.
 18. The tracking servo circuit of claim 17,wherein said coefficient setting means comprises:an address generator;and a coefficient memory.
 19. A tracking servo circuit of an opticaldisk player having a tracking actuator for displacing an informationreading optical spot in the radial direction of an optical disk withrespect to a track of the optical disk along which the information isread, the tracking servo circuit operative to execute drive control ofsaid tracking actuator according to a tracking error signal,comprising:a digital filter for alternately extracting from saidtracking error signal a frequency component within a specified band anda high-frequency component according to coefficient values set up withinsaid digital filter; actuator control means for applying a braking forceto said tracking actuator in response to said high-frequency componentwhen a brake ON command is issued; an address generator coupled to acoefficient memory operative to set up the coefficient values in saiddigital filter depending on whether said brake ON command is issued; afirst gate having an output coupled to an input of the addressgenerator; an inverter having its output coupled to a first input of thefirst gate; a register operative to receive and store an anti-shockcontrol command, a brake control command and at least two tracking gaincontrol commands, the register having an anti-shock control commandoutput coupled to a second input of the first gate and a brake controlcommand signal output coupled to an input of the inverter; and a secondgate having a first input coupled to a first tracking gain commandoutput of the register and a second input coupled to a second trackinggain command output of the register.